A study of sialon synthesis from kaolin by carbothermal reduction and simultaneous nitriding

X-ray diffraction, derivatographic analysis, and the BET method are used to study the processes of synthesis of sialons by carbothermal reduction and simultaneous nitriding of kaolin of the Kyshtymskoe deposit. The synthesis is performed by roasting a mixture of kaolin with colloidal graphite S-1 poured freely or pressed into specimens in a discontinuous-flow furnace with a graphite heater. The influence of the synthesis conditions on the phase composition, the specific surface of the powders, the gas permeability, and the pore size in sialon specimens is established. It is shown that when pressings fabricated from kaolin mixed with graphite S-1 are roasted in nitrogen, the resulting material can have a porosity of 60% with pores < 1 mum in size and a gas permeability of 0.02 - 0.08 mum(2), which can become a basis for developing a technology of membrane materials.